Research On Identification Of Seat Vibration Source Affecting Excavator Driver’s Vibration Comfort

Comfort is an important aspect for users to judge vehicle performance. Due to the harsh operating environment, drivers of the excavator have to suffer high-intensity of vibration, which makes the vibration comfort issue become an outstanding problem. Along with the human-body-allowed vibration limits, which are specified in lots of relevant national vibration standards, have been constantly strict, it has been an urgent problem to control the vibration intensity that drivers suffering and improve the excavator’s vibration comfort. Seat vibration, as a decisive factor for driver’s vibration comfort, is the most important object to be controlled while conducting comfort research. Excavator has a complex whole-structure system and contains plenty of vibration sources, and the seat vibration is affected by multiple of them. Therefore, to make sure the major sources and their transmission pathways is a much more effective way of controlling the seat vibration.Basing on a practical engineering project, this thesis focuses on a certain type of crawler hydraulic excavator and conducts a research on finding out the major sources and their transmission pathways that mainly affect the vibration comfort. This study, begin with the seat vibration, discusses the vibration comfort evaluation method for excavator, and provides a blind source identification and source contribution calculation method which are suitable for excavator seat vibration signals. For two seat vibration signals from the tested excavator have exceeded the vibration comfort limits, this proposed method is applied to them attempting to find the major vibration sources and their transmission pathways. After analyzing, some conclusions are summarized.Firstly, as human comfort perception varies from different vibration components, the vibration response signals between chair surface and human-body ischium protrusion are regarded as the objects of this research. Currently, there is lack of evaluation criterion for excavator’s vibration comfort, however, it is an important prerequisite for following vibration source identification to evaluate and find out the comfort exceeded seat vibration components in certain engine speed. Therefore, this study makes a deep research on common comfort evaluation standards and finds that the common method named total vibration evaluation cannot characterize excavator driver’s comfort perception, but the frequency-weighted acceleration evaluation method basing on each axial of vibrations is much more suitable for the excavator seat vibration comfort evaluation. The test for vibration signals collecting is designed, and the provided frequency-weighted acceleration method is applied to evaluate comfort status of the tested excavator, then the seat vibration components which exceed comfort limits are located.Secondly, facing to the shortcomings of Second Order Blind Identification method in processing single observation signals which are similar to the seat vibration signals, this study takes the Ensemble Empirical Mode Decomposition technic as a signal preprocessing method and proposes a new seat vibration source identification method called combined EEMD and SOBI, which makes it possible to convert one-dimension signal to multi-dimension observation matrix. However, this method still has two problems:one is that it is unable to show the contribution of each estimated source and the other is that it is unable to exclude the meaningless components after EEMD. After a series of analysis, some measurements have been taken out:the proposed contribution matrix can calculate the contribution of each estimated source, the proposed energy contribution rate together with the correlation coefficient analysis can help to select useful IMFs. The specific algorithm processing of this combined method is summarized, and the validity and correctness of this method are verified by the analysis on simulation signals.Finally, the proposed combined method is applied to the testing chair vibration signals which exceed the comfort limits. After a series of processing (decomposition, vibration source estimation and source contribution calculation), the features of target sources which may affect comfort most are confirmed. The Short-time Fourier time-frequency analysis technic is applied to get the time-frequency feature of estimated sources. Combined with the prior knowledge of excavator and the time-frequency diagrams of the tested source signals, the definite sources which mainly cause seat vibration can be find out, so as the main vibration transmit pathways.This thesis focuses on the comfort exceeded seat vibration signals of the objective excavator under two operating speed, the results show that:a periodic excitation force caused by the engine cylinder ignition explosions is the main factor that influence the seat comfort, and the main frequency components are mainly passing through several specific points of the four-point fulcrums which supporting the engine. Therefore, the measurement of modifying damping performance of the engine supporting rubber damper at low frequencies, especially at the ignition frequency, should be taken and which would be an effective way to reduce the seat vibration acceleration and get driver’s vibration comfort improved.